In recent years, it has become increasingly desirable for Mobile Network Operators (MNOs) to integrate their cellular and non-cellular (e.g. Wi-Fi) networks. This provides a mechanism for the MNO to both offload cellular data traffic onto a Wi-Fi network having a wired data connection (which is generally more suited to high data demands) and “onload” traffic seamlessly back onto the cellular network. Accordingly, modern cellular technologies, such as the 3rd Generation Partnership Project (3GPP) LTE networks, have evolved to include a tight integration between the cellular and non-cellular networks, such that handovers between the two networks are correctly authenticated and maintain consistent policy and charging control.
4G network standards provide a framework for interconnecting the non-cellular (commonly known as “non-3GPP”) network and the Evolved Packet Core (EPC) through the trusted and untrusted access specification (as specified in 3GPP Technical Specification 23.402 Release 12 Architectural Enhancements for Non-3GPP Access). The standards do not strictly define when a non-3GPP network is trusted or not (this is at the discretion of the MNO), but they do define how the MNO must treat the traffic—the principle difference being that untrusted non-3GPP connections must include an Internet Protocol Security (IPSec) tunnel between the User Equipment (UE) and the EPC. For trusted networks, communication between the UE and EPC is considered secure (e.g. by using subscriber identity module, or SIM, based authentication with the UE and WPA2 IEEE 802.11i-2004 security in the Wi-Fi Access network).
Most of today's networks (e.g. 2G and 3G networks) predate the 4G standards. However, it is still desirable for MNOs to integrate the non-3GPP and pre-4G cellular networks. To make this possible, a Wireless Access Gateway (WAG) is used to interconnect the two networks. The WAG connects to the cellular network using the General Packet Radio Service (GPRS) Tunneling Protocol (GTP) connecting directly to a Gateway GPRS Support Node (GGSN). However, the data connection between the WAG and the non-3GPP network is not standardized. Accordingly, a variety of methods for routing user plane data from a non-3GPP network to the cellular network have been used. These existing methods can be grouped into Layer 2 or Layer 3 integration. Layer 2 integration can be complicated to implement, requiring the WAG to become part of the Wireless Access Network. This increases the cost of deployment for a Wi-Fi Network operator. Thus, the distributed architecture of Layer 3 integration (in which the WAG is a separate component in the network) is more desirable.
In Layer 3 integration, the user plane internet protocol (IP) traffic is routed from the Wi-Fi Network's Wireless LAN Controller (WLC) to the WAG, and then from the WAG to the cellular network. The key issue with the Layer 3 approach is associating the IP address for the UE in the non-3GPP network with the IP address for the UE in the cellular network. There are several techniques, including the following two examples. Firstly, the ‘Radius Framed-IP-Address’ technique involves the AP allocating an IP address for a User Equipment (UE) and subsequently informing the WAG of this IP address using the RADIUS signaling message. Secondly, the ‘DHCP Relay’ technique involves the DHCP request message issued by the WAG being ‘relayed’ to the WAG, and the WAG issuing the IP address for the UE. The WAG may then set up the appropriate routing rules with the IP address in the cellular network.
The Cisco enhanced Wireless Access Gateway (eWAG) is an example of a Layer 3 integration of the WAG. An example of the eWAG can be found at www.cisco.com. In the Cisco system, an Access Point allocates the IP address in the Wi-Fi domain for the UE, and supplies this IP address to the eWAG as part of the Framed-IP-Address element of the RADIUS Accounting Start message. The MNO supplies the IP address in the cellular domain, and the eWAG sets up the appropriate routing rules.
The present inventors have identified several problems with the existing techniques. Firstly, the 3GPP standards specify that the MNO must allocate the IP address for the UE, which is then routed to the corresponding IP address for the UE in the non-3GPP domain by the WAG. However, if the WAG is connected to multiple MNOs, the MNOs may issue the same IP address for the same UE. This creates an issue when the WAG routes IP traffic from the UE to the cellular network, as it cannot differentiate between the two MNOs for that IP address. Secondly, the IP address issued to the UE in the non-3GPP domain may conflict with an IP address for another UE connected to the AP. This may happen, for example, when the IP address in the non-3GPP domain is issued by the WAG. This IP address conflict will create an issue when the WAG routes IP traffic to the UE in the non-3GPP domain, as the same IP address is associated with two UEs.
Furthermore, the prior art techniques provide a method of setting up a data path between the UE and cellular data network, but this data path must be torn down if the UE roams out of the non-3GPP network (e.g. onto a distinct non-3GPP network). Thus, IP address sensitive applications cannot continue to function when the UE roams between non-3GPP networks.
It is therefore desirable to alleviate some or all of the above problems.